As the number of peripherals users attach to their computer systems proliferate, the more dense the tangle of cables around the computer becomes.
Besides being bulky, cables also limit the maximum distance the peripherals may be located from the computer. Peripheral manufacturers have addressed these problems by communicating commands and data through electro-magnetic (EM) pulses which do not require any type of physical connection between the peripheral and the computer. Electro-magnetic communication requires two electronic circuits. The first, called an EM transmitter, converts electrical signals into EM pulses and broadcasts the EM pulses into the atmosphere. A corresponding electronic circuit, called an EM receiver, collects the pulses and converts them back into electrical signals. In theory, EM communication could use infrared (IR) light, radio frequency (RF) waves, or any other portion of the electro-magnetic spectrum. As a practical matter, however, only IR and RF are suitable for computer communication without causing or being impeded by interference from other radiation sources. Most manufacturers have chosen to implement EM technology using IR but the following discussion applies to RF as well.
The most basic IR connection is used in one-way communication: the computer sends commands and data to the peripheral but the peripheral does not send information back to the computer. A one-way IR communication link has an IR transmitter coupled to the data bus of the computer and an IR receiver coupled to the input line of the peripheral device. The IR transmitter converts the standard electrical signals representing commands and data for the device into pulses of infrared light and transmits those pulses across some distance to the IR receiver. The IR receiver then converts the pulses back into standard electrical signals and passes them onto the device where they are acted upon as either commands or data.
A more complicated IR connection provides for bi-directional communication between the computer and the peripheral, so the computer and the device must each have both an IR transmitter and an IR receiver. In such cases, the IR transmitter and IR receiver circuitry is usually combined into a single unit called an IR transceiver.
Until recently, all IR-equipped peripherals used proprietary technology so each device required its own unique IR transceiver connected to the computer. In 1994, however, an industry organization called the Infrared Data Association (IRDA) proposed an IR standard that promotes compatibility among IRDA compliant devices. Such compatibility allows a computer with a single IRDA transceiver to communicate with multiple IRDA devices such as printers, modems, fax machines, and even other IRDA-equipped computers. The IRDA standard also specifies error checking and correction protocols and enables a 9600 KB to 4 MB per second transfer rate.
If using proprietary IR circuitry, a peripheral manufacturer provides an external unit containing the corresponding proprietary IR circuit for the computer. This external unit, often referred to as a "dongle", interfaces to the computer by means of a cable connected through a serial, or other suitable, port. Since the IRDA standard was promulgated, many vendors have announced they will build IRDA compliant computers but existing computer users want the advantages offered by IRDA. Therefore, a dongle incorporating the IRDA specification will be an important add-on device for many computers.
By using IRDA compliant peripherals and an IRDA dongle, users can reduce the number of peripheral cables they have connected to their computer. However, the IRDA dongle does not completely eliminate all peripheral cables since it itself requires a cable connected to a serial port. Also, most users have a pointing device connected by another cable to the computer, usually to a serial port, and a keyboard connected by yet another cable. The need to connect the IRDA dongle and the pointing device through separate serial ports impairs the user's ability to attach other serial devices as most computers are configured with only two serial ports. A further limitation of the IRDA dongle is that it competes with the pointing device for space in the user's often crowded work area. Thus, there is a need to reduce the space required for such dongles.